package bookings

import (
	"context"
	"errors"
	"sort"
	"time"

	"github.com/jackc/pgx/v5"

	"bookra/apps/backend/internal/db"
)

// PromoteWaitlist confirms the earliest waitlisted bookings on a class session
// while free capacity remains. It returns the promoted records so callers can
// notify customers. A missing session is treated as nothing to promote.
func PromoteWaitlist(ctx context.Context, repo db.Repository, tenantID, sessionID string) ([]db.BookingRecord, error) {
	session, err := repo.GetClassSessionByID(ctx, sessionID)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, nil
		}
		return nil, err
	}

	bookings, err := repo.ListBookingsBySession(ctx, sessionID)
	if err != nil {
		return nil, err
	}

	confirmed := 0
	var waitlisted []db.BookingRecord
	for _, booking := range bookings {
		switch booking.Status {
		case "confirmed":
			confirmed++
		case "waitlisted":
			waitlisted = append(waitlisted, booking)
		}
	}
	if len(waitlisted) == 0 {
		return nil, nil
	}
	sort.SliceStable(waitlisted, func(i, j int) bool {
		return waitlisted[i].CreatedAt.Before(waitlisted[j].CreatedAt)
	})

	var promoted []db.BookingRecord
	for _, booking := range waitlisted {
		if session.Capacity > 0 && confirmed >= int(session.Capacity) {
			break
		}
		if err := confirmWaitlistedBooking(ctx, repo, tenantID, booking); err != nil {
			return promoted, err
		}
		confirmed++
		promoted = append(promoted, booking)
		_ = repo.AppendActivityEvent(ctx, db.ActivityEventParams{
			TenantID:   tenantID,
			ActorKind:  "system",
			Action:     "booking.promoted",
			EntityType: "booking",
			EntityID:   &booking.ID,
			Summary:    booking.CustomerName + " — " + session.Title,
		})
	}
	return promoted, nil
}

// PromoteBooking manually confirms one waitlisted class booking. Unlike the
// automatic FIFO promotion it targets a specific booking; when the session is
// full it fails with ErrSessionFull unless allowOverCapacity is set — a
// deliberate business override, not a silent overbooking.
func PromoteBooking(ctx context.Context, repo db.Repository, tenantID, bookingID string, allowOverCapacity bool) (db.BookingRecord, error) {
	booking, err := repo.GetBookingByID(ctx, bookingID)
	if err != nil {
		return db.BookingRecord{}, err
	}
	if booking.TenantID != tenantID {
		return db.BookingRecord{}, pgx.ErrNoRows
	}
	if booking.Status != "waitlisted" || booking.ClassSessionID == nil {
		return db.BookingRecord{}, ErrNotWaitlisted
	}
	sessionID := *booking.ClassSessionID

	if !allowOverCapacity {
		session, err := repo.GetClassSessionByID(ctx, sessionID)
		if err != nil {
			return db.BookingRecord{}, err
		}
		sessionBookings, err := repo.ListBookingsBySession(ctx, sessionID)
		if err != nil {
			return db.BookingRecord{}, err
		}
		confirmed := 0
		for _, other := range sessionBookings {
			if other.Status == "confirmed" {
				confirmed++
			}
		}
		if session.Capacity > 0 && confirmed >= int(session.Capacity) {
			return db.BookingRecord{}, ErrSessionFull
		}
	}

	if err := confirmWaitlistedBooking(ctx, repo, tenantID, booking); err != nil {
		return db.BookingRecord{}, err
	}
	booking.Status = "confirmed"
	return booking, nil
}

// confirmWaitlistedBooking flips a waitlisted booking to confirmed and
// re-arms reminder jobs — a booking promoted after its reminder already
// dispatched-as-skipped would otherwise go unreminded.
func confirmWaitlistedBooking(ctx context.Context, repo db.Repository, tenantID string, booking db.BookingRecord) error {
	if err := repo.UpdateBookingStatus(ctx, booking.ID, "confirmed"); err != nil {
		return err
	}
	RearmReminderJobs(ctx, repo, tenantID, booking)
	return nil
}

// RearmReminderJobs clears pending reminders for a booking and re-arms them
// for its (possibly new) start time. Used after promotion, session moves, and
// schedule retimes so reminders always match the booking's live window.
func RearmReminderJobs(ctx context.Context, repo db.Repository, tenantID string, booking db.BookingRecord) {
	_ = repo.DeletePendingReminderJobsForBooking(ctx, booking.ID)
	_ = armReminderJobs(ctx, repo, tenantID, booking.ID, booking.StartsAt, booking.CustomerPhone)
}

// armReminderJobs schedules the email reminder — and the SMS reminder when the
// tenant opted into SMS and a phone number is on file — for a booking whose
// start still falls inside a reminder horizon. A start too close or too far
// away simply arms nothing.
func armReminderJobs(ctx context.Context, repo db.Repository, tenantID, bookingID string, startsAt time.Time, customerPhone string) error {
	scheduledFor, ok := reminderSchedule(startsAt)
	if !ok {
		return nil
	}
	if err := repo.CreateReminderJob(ctx, db.ReminderJobParams{
		TenantID:     tenantID,
		BookingID:    bookingID,
		Channel:      "email",
		ScheduledFor: scheduledFor,
	}); err != nil {
		return err
	}
	if customerPhone != "" {
		if smsSettings, err := repo.GetTenantSMSSettings(ctx, tenantID); err == nil && smsSettings.Enabled {
			_ = repo.CreateReminderJob(ctx, db.ReminderJobParams{
				TenantID:     tenantID,
				BookingID:    bookingID,
				Channel:      "sms",
				ScheduledFor: scheduledFor,
			})
		}
	}
	return nil
}